Sacrificial energy dissipation mechanism

ABSTRACT

Structural devices for energy dissipation can be designed to provide asymmetrical responses to cyclic axial loading. The energy dissipation devices can be designed to provide a known or predictable response to tensile loading, along with a different known or predictable response to compressive loading. The devices may include a filament which bears a portion of both tensile and compressive loads and a bracing device which provides lateral support to the filament to prevent buckling. Interlocks or a similar restraining mechanism can be used to resist part of either a compressive or tensile load. These components can be configured in such a manner as to provide an asymmetric response.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 62/176,887, filed Aug. 9, 2014, thedisclosure of which is hereby incorporated by reference.

BACKGROUND

1. Technical Field

This disclosure relates to energy dissipation devices which can be usedin structural engineering.

2. Description of the Related Art

Often, it is necessary to control the physical response of a mechanicalor structural system from some dynamic excitation. This can be donethrough the use of materials with inelastic behaviors. In buildings, forinstance, certain regions of the building may be designed as “structuralfuses” that become damaged during a high-intensity seismic event. These“fuses” can be constructed of steel or reinforced concrete and detailedsuch that they deform in a ductile manner, dissipating energy during adynamic motion. An example of one of these “fuse” types is the bracedframe. There are several well developed, and quite effective, types ofstructural “fuses” used in structural and mechanical system design. Mosthave a similar behavior when loaded in either of two possible directions(e.g. tension/compression, positive/negative bending, etc.) This type ofbehavior is described herein as having a symmetric load-deformationbehavior.

Some applications have a need for an asymmetric load-deformationbehavior. As an example, a pre-engineered metal building can use steelmoment frames to resist lateral building loads in the buildingtransverse direction. Most metal buildings are lightweight, and thustheir structural member sizes are controlled by load demands fromnon-seismic types of loading, such as snow or roof dead load. Researchhas shown that these types of structures lack the level of ductilityoften found in traditional column-and-beam steel frames. An attempt atusing a traditional steel plastic hinge would place a symmetric behaviorhinge near the column-to-rafter joint, but as the bending moments fromsnow and dead load often exceed those from the expected seismic demands,sizing the plastic hinges for seismic demands would result in failureunder those other loadings. Stronger plastic hinges, sized for thecontrolling load cases, would result in a lack of energy dissipationduring seismic excitation. Therefore, this application would benefitfrom an energy dissipation device that would provide sufficient strengthand stiffness to resist non-seismic loads, while still deformingsignificantly under seismic demands, such as an energy dissipationdevice with an asymmetric load-deformation behavior.

The concentric braced frame is an example of an energy dissipationsystem that has an asymmetric load-deformation behavior. It is designedto yield in tension. However, it buckles in compression. Due to the highlocal strains caused by buckling, cyclic loading of the concentricbraced frame tends to result in low-cycle fatigue cracking. Also, thepost-buckling strength and stiffness of the brace is difficult topredict and typically a source of high uncertainty in design.

Another type of lateral load resisting system formed from asymmetricallybehaving components is the tension-only brace. This type of brace, madefrom slender rods or cables, has effectively no compression strength,and therefore must be used in pairs (e.g. an X-configuration) to providebi-directional strength and stiffness. The tension-only braces do nottypically provide energy dissipation, only linear elastic strength andstiffness to resist lateral forces on the buildings. If they were toyield, the rods/cables would elongate and effectively result in anunsupported structure when the building returned to its originalconfiguration. Neither of these types of devices provides a reliable andductile asymmetric load-deformation behavior.

SUMMARY

In one embodiment, an energy dissipation device can include a firstretaining member, the first retaining member defining a first receivingspace, a second retaining member, the second retaining member defining asecond receiving space, a filament extending along a longitudinal axisthrough the first and second receiving spaces, the filament secured at afirst end to the first retaining member and secured at a second end tothe second retaining member, at least one of the first and secondretaining members being configured to constrain longitudinal translationof the first and second retaining members relative to one another toprovide an asymmetric force-displacement response to an induced axialload.

In one aspect, the second retaining member can be configured to at leastpartially extend into the first receiving space of the first retainingmember, and at least one of the first and second retaining members caninclude a stop configured to inhibit removal of the second retainingmember from the first receiving space of the first retaining member.

In one aspect, the first receiving space of the first retaining membercan include a deformation region in which the cross-sectional size ofthe first receiving space allows for the lateral translation of thesecond retaining member from the second receiving space into the firstreceiving space when a compressive axial load is applied to the device.

In one aspect, a first end of the first retaining member can beconfigured to abut a first end of the second retaining member to inhibitfurther longitudinal translation of the first and second retainingmembers either towards or away from one another, depending on thedesired geometric configuration.

In one aspect, the first retaining member can include a first set ofparallel plates and the second retaining member can include a second setof parallel plates, and the second retaining member can be configured toat least partially extend into the first receiving space of the firstretaining member. In a further aspect, the filament and each of theplates in the first and second sets of parallel plates can an apertureextending therethrough, and the longitudinal dimensions of the aperturesin the first set of parallel plates can be larger than the longitudinaldimensions of the apertures in the second set of parallel plates.

In one aspect, the device can additionally include a first end-capsecured to the first retaining member and the first end of the filament,and a second end-cap secured to the second retaining member and thesecond end of the filament.

In another embodiment, an energy dissipation device configured toprovide an asymmetric response to axial loading can include an axialmember extending in a longitudinal direction between a first endcap anda second endcap, a bracing mechanism enclosing at least a portion of theaxial member, the at least one bracing member providing lateral supportto the axial member to inhibit buckling when the axial member is under acompressive load, a restraining mechanism configured to engage anothercomponent of the device to limit longitudinal translation of the firstand second endcaps relative to one another, such that other componentsof the device bear a portion of the axial load when the restrainingmember is engaged with another component of the device.

In one aspect, the bracing mechanism can include first and secondretaining members, where the first endcap includes or is coupled to thefirst retaining member and the second endcap includes or is coupled tothe second retaining member, where the first retaining member encloses aportion of the axial member adjacent the first endcap, and where thesecond retaining member encloses a portion of the axial member adjacentthe second endcap. In a further aspect, at least one of the first andsecond retaining mechanisms can include a contact surface which servesas the restraining mechanism and is configured to engage a portion ofthe other of the first and second retaining mechanisms to limit lateraltranslation of the first and second retaining mechanisms and allow thefirst and second retaining mechanisms to bear a portion of an axial loadapplied to the device. In one still further aspect, the contact surfacecan include a surface of the first retaining member facing the secondendcap and configured to abut a facing surface of the second retainingmember to allow the first and second retaining mechanisms to bear aportion of a compressive axial load applied to the device. In anotherstill further aspect, the contact surface can include a surface of thefirst retaining member facing the first endcap and configured to engagean interlocking surface of the second retaining member to allow thefirst and second retaining mechanisms to bear a portion of a tensileaxial load applied to the device.

In one aspect, the restraining mechanism can be independent of thebracing mechanism. In a further aspect, the restraining mechanism caninclude a second axial member extending through an aperture in one ofthe first or second endcaps, and at least one stop coupled to the secondaxial member, where the apertures in one of the first or second endcapsis located between the of stop and the other of the first or secondendcaps, and where a cross-sectional dimension of the stop is largerthan a cross-sectional dimension of the apertures such that the stopabuts an outer surface of the endcap including the apeture to limitlongitudinal translation of the endcaps away from one another.

In another embodiment, a structural and/or mechanical energy dissipationdevice can include a first end-cap, a second end-cap, a filamentextending between the first end-cap and the second end-cap, the filamentincluding a material having nonlinear mechanical properties, a filamentbracing component, and a restraining component including at least onecontact surface configured to contact another portion of the device tolimit further translation of the first end-cap relative to the secondend-cap to provide an asymmetric force-displacement response to aninduced axial load.

In one aspect, the first end cap can be rigidly attached to therestraining component and the second end cap can be movable over alimited range with respect to the restraining component. In one aspect,a first cross-sectional dimension of the filament can be at least twiceas large as a second cross-sectional dimension of the filament. In oneaspect, filament bracing component includes at least two cantileveredmembers rigidly attached to the first end-cap, where a length of the atleast two cantilevered members is less than a length of the filament butat least half the length of the filament. In one further aspect, thedevice can additionally include at least two cantilevered membersrigidly attached to the second end-cap, where the at least twocantilevered members, and where the at least two cantilevered membersrigidly attached to the first end-cap and the at least two cantileveredmembers rigidly attached to the second end-cap are configured to befreely translatable past one another when an axial load is applied tothe device. In another further aspect, the filament can include at leastone of a metal, a shape memory alloy, or a composite material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of one embodiment of an energydissipation device which is configured to be stronger and stiffer intension than in compression.

FIG. 2 illustrates a cross-sectional view of an energy dissipationdevice which is configured to be stronger and stiffer in compressionthan in tension.

FIG. 3 illustrates the operation of the energy dissipation deviceembodiment illustrated in FIG. 1 under compression, in which the innerinterlocks recess into a deformation chamber located within the spacesdefined by the position of the outer interlocks

FIG. 4 illustrates another embodiment of an energy dissipation devicewith an alternative interlock design to provide a similar performance tothat of the embodiment illustrated in FIG. 1, using a left and rightinterlock instead of an inner or outer interlock

FIG. 5 illustrates another embodiment of an energy dissipation devicewhich provides similar performance to that of the embodiment illustratedin FIG. 1, using a bolt and slotted holes instead of flanged interlocks.

FIG. 6 illustrates another embodiment of an energy dissipation devicewhich provides similar performance to that of the embodiment illustratedin FIG. 1, using interlocks which do not provide lateral restraint tothe filament, instead using additional components to provide the lateralrestraint to the filament.

DETAILED DESCRIPTION

Embodiments of energy dissipation devices described herein provide anasymmetric load-deformation behavior, through the use of severalcomponents, which can be configured to provide a larger strength andstiffness in either tension or compression. In addition, buckling isprevented through continuous bracing of the deformable element. Finally,both configurations of the device can allow the tension and compressionstrength and stiffness to be purposefully designed with a high degree ofcertainty for both tension and compression.

Embodiments of energy dissipation devices which exhibit the intendedasymmetric strength and stiffness described herein can be constructed inmany possible configurations. Two exemplary configurations are describedherein to demonstrate the concept. Both of these example configurationsinclude a combination of certain elements: a filament or similardeformable element, interlocks which provide strength and stiffness,filament bracing components, and end-caps or similar connectiveelements. The filament is the deformable portion of the device,undergoing inelastic deformations to dissipate energy. The interlocks,configured in various ways, contribute to either the tensile orcompressive strength and stiffness, dependent upon the particularconfiguration. The filament bracing components provide lateral bracingto the filament to prevent buckling, which would cause low-cyclefatigue. The end-caps connect all the components together and provideattachment points to the mechanical or structural system of application.It will be understood that the elements described in the two exampleconfigurations are merely exemplary, and that other embodiments mayinclude additional or fewer elements. For example, elements other thanend-caps may be used to attach the energy dissipation device tosurrounding structural or mechanical components. As another example, thefunction of the interlocks may, instead, be performed by othermechanisms, including bolts, cables, rods, plates, or other feasiblemethods.

In reference to the aforementioned metal building application thisdevice could be attached in place of a beam-to-column knee joint webplate, in a diagonal truss configuration. The parts and pieces could beconfigured to provide a high strength and stiffness when under snow orroof dead load and a weaker strength when the loads are reversed due toa seismic event. This is only one of many potential applications of theembodiments described herein.

FIG. 1 illustrates a cross-sectional view of an energy dissipationdevice which is configured to be stronger and stiffer in tension than incompression. This energy dissipation device 100 includes a filament 110extending through the receiving spaces 122 and 132 defined by thepositions of the outer interlocks 120 and inner interlocks 130. Withinreceiving space 122 exists a deformation chamber 126 which defines thespace whereupon inner interlocks 130 translate into receiving space 122.

The filament 110 may include a rod formed from an inelasticallydeformable material. In some embodiments, this material may be metallic.The filament 110 extends between two end-caps 140 and 150. In someembodiments, the filament 110 can be positively attached to the end-caps140 and 150, such as through the use of weldament, although otherconnection types and methods can be used.

The cross-section (in a plane normal to the longitudinal axis of thefilament 110) of the filament 110 can be of any suitable geometry,having dimensions appropriate to satisfy the particular designrequirements for a given instance of application. The cross-section ofthe filament 110 may vary along its length. In some embodiments, thefilament may have a circular cross-section, a square cross-section, or arectangular cross-section, although any other suitable shapes anddimensions may be used. In some embodiments, the filament may be aplate, having a first cross-sectional dimension (e.g., width) that canbe substantially larger than the second cross-sectional dimension (e.g.,height). For example, in some implementations the first cross-sectionaldimension may at least be 2, 3, 5, or 10 times as large as the secondcross-sectional dimension, although any suitable ratio may be used. Whenthe first cross-sectional dimension is sufficiently larger than thesecond-cross-sectional dimension, bracing to prevent buckling of thefilament 110 may be provided primarily or exclusively on either side ofthe shorter dimension of the filament 110, as the increased thickness ofthe longer dimension will provide resistance to buckling.

In some embodiments, the geometry and material of the filament 110 arechosen such that filament 110 will provide a sustained integrity ofstrength and stiffness, through multiple cycles of large compressive andtensile deformations, as required by the particular application, so asto prevent low-cycle fatigue cracking and rupture of the filament 110,such that a desired response can be designed into the particularembodiment with a high degree of reliability. In some embodiments, thefilament 110 may be formed from or may include a material which hasnonlinear mechanical properties. In some specific embodiments, thefilament 110 may be formed from a metal such as steel, or from a shapememory alloy, or from a composite material such as a carbon fibermaterial, although a wide range of alternative materials may also beused, depending on the particular embodiment.

The outer interlocks 120 and inner interlocks 130 are a set oflongitudinally-extending and interlocking elements which, in conjunctionwith the location of filament 110, define interior receiving spaces 122and 132, respectively, and border the filament 110 along its length andare positively attached to end-caps 140 and 150. Only the outerinterlocks 120 or inner interlocks 130 are attached to each end-cap,typically by weldament, with the outer interlocks 120 being attached tothe end-cap 140 and the inner interlocks 130 being attached to theend-cap 150. In some embodiments, there may exist multiple pairs ofinner and outer interlocks 120 and 130 or multiple tensile members suchas rods surrounding the filament 110, as illustrated in FIG. 6.

Some or all of the outer interlocks 120 and inner interlocks 130 caninclude a structural feature configured to constrain longitudinaltranslation of the outer interlocks 120 relative to the inner interlocks130. This structural feature may include a geometrical means ofinterlocking, in various embodiments, such as a pair of flanges, a slotand stud pair, nuts on the ends of threaded rods extended through theend-caps 140 or 150 or any other suitable structural feature. In someembodiments, the structural feature may include a contact surfaceconfigured to engage, interlock with, abut, or otherwise come intocontact with another component of the device. In the embodimentillustrated in FIG. 1, the outer interlocks 120 include an inwardlyextending flange 124 and the inner interlocks 130 include an outwardlyextending flange 134. In this embodiment, the flanges 124 and 134 do notprevent longitudinal translation of the interlocks 120 and 130 towardsone another in such a manner as to cause the mutual separation offlanges 124 and 134, but instead constrain longitudinal translation ofthe interlocks 120 and 130 away from one another in such a manner as tocause the mutual contact of flanges 124 and 134, thereby placing theinterlocks 120 and 130 into tension.

The function of the filament bracing components in the basic deviceconfiguration illustrated in FIG. 1 is performed by the interlocks 120and 130. The interlocks 120 and 130 are separate from, but may be incontact with, the filament 110 along its length to provide lateralrestraint to the filament 110 whilst the filament 110 is in compression.The cross-sections (in a plane normal to the longitudinal axis of thedevice) of the interlocks 120 and 130 and of the interior receivingspaces 122 and 132 can be of any suitable geometry, having dimensionsappropriate to satisfy the particular design requirements for a giveninstance of application and to provide any necessary lateral restraintto the filament 110 along its length. The interlocks 120 and 130 can beformed from any material appropriate to satisfy the particular designrequirements for a given instance of application. In some embodiments,the interlocks 120 and 130 may be metallic, however it is conceivablethat other materials, such as plastics, composites, ceramics, woods, orother material types, may be utilized in design and fabrication of theinterlocks 120 and 130. As noted above, the structural features thatprovide points of contact between the interlocks 120 and 130, whichprovide unique behavioral characteristics of the device 100, may take onmany various forms which may depend on the particular designrequirements for a given instance of application, most notably, theselected basic device configuration illustrated in FIG. 1.

The end-caps 140 and 150 are connector pieces which can serve twopurposes: to provide attachment points to the dynamical system to whichthe device 100 is to be attached, and to provide a base of attachment ateach end of the device 100 such that the interlocks 120 and 130 and thefilament 110, together, form an interconnected system. The end-caps 140and 150 can be of any suitable geometry and material, having propertiesto satisfy the particular design requirements for a given instance ofapplication. In some embodiments, each pair of end-caps 140 and 150 canbe identically constructed, while in other embodiments the end-caps maybe differently constructed. In some embodiments, some form of flexuralmoment release (such as a pin-type hinge or a universal joint) will beincluded in the geometry of each end-cap 140 and 150 such that thedevice acts to primarily resist axial deformations.

Thus, the device 100 of FIG. 1 is stronger and stiffer in tension thanin compression. The interlocks 120 and 130 are configured such that theywill freely longitudinally translate along one another's longitudinalaxis, as shown in FIG. 3, when the device 100 is compressed. Thus, theonly longitudinal element undergoing compressive stress, in thisparticular embodiment, is the filament 110.

The deformation chamber 126 is a void between the outer interlocks 120and the filament 110 that allows the inner interlocks 130 to recess intoreceiving space 122 unimpeded by the presence of outer interlocks 120.The deformation chamber 126 can have a longitudinal dimensionappropriate to allow the expected maximum compressive deformation of thefilament 110. This dimension will be determined as appropriate to meetthe particular design requirements for a given instance of application.In some embodiments, the length of the deformation chamber 126 can bedesigned such that it is as short as feasible so as to provide themaximum length of lateral restraint for the filament 110, although inother embodiments longer deformation chambers 126 may be used

Note that the interlocks 120 and 130 may be constructed from multipleparts that convolute the distinction between the “outer” and “inner”descriptors. One possible example of this convolution is depicted inFIG. 4. FIG. 4 illustrates an alternate embodiment of an energydissipation device. The energy dissipation device 400 includes afilament 410, end-caps 440 and 450, and symmetrical interlocks 420. Thefilament 410 in the illustrated embodiment is a planar structure havinga longitudinal axis extending between caps 440 and 450. The interlocks420 are two pairs of L-shaped structures having flanges 424 extendingperpendicular to the longitudinal axis of the filament 410. The flanges424 of one interlock interact with one another when the structure is intension to prevent longitudinal translation of the interlocks 420 awayfrom one another. Additional alternative embodiments of the interlocksare possible.

FIG. 5 illustrates another embodiment of an energy dissipation devicewhich uses a bolt and slotted holes instead of flanged interlocks. Thefilament 510 is a planar structure having a longitudinal axis extendingbetween caps 540 and 550. Unlike the planar filament 410 of FIG. 4,however, the filament 510 includes a longitudinally extending slot 516extending therethrough. The longitudinally extending slot 516 may insome embodiments be centered and aligned with the longitudinal axis ofthe filament 510. The inner interlock 530 is a pair of parallel platesdefining a receiving space for the filament 510, each of which includesa longitudinally extending slot 536 which can be aligned with thelongitudinally extending slot 516 in filament 510. The outer interlock520 includes a pair of parallel plates defining a receiving space forthe inner interlock 530, each of which includes a hole 526 which islongitudinally shorter than the longitudinally extending slots 536 and516. When a member such as a bolt, rod, pin or stud 524 is insertedthrough the hole 526 and slots 516 and 536, the stud 524 will constrainmovement of the outer interlock 520 relative to the inner interlock 530,with the difference in longitudinal length between the hole 526 and theslots 516 and 536 permitting some longitudinal translation.

Each of the configurations illustrated and described herein includefilament bracing components designed to provide adequate lateralrestraint to the filament to prevent said filament from buckling incompression. This function may be performed by the interlocks 120, 130,420, 520, or 530, or by separate alternative components such as FIG. 6′sfilament bracing components 620, discussed in greater detail below Thequantified adequate lateral restraint can be determined via structuralmechanics and can consist of both strength and stiffness requirements.

The interlocks 120, 130, and 420, 520, or 530, depicted in and describedwith respect to the devices 100, 400, and 500 include a mechanism toprovide contact between the interlock pairs when the device is placedinto tension. This contact mechanism can take the form of a pair offlanges 124, 134, and 424, a slot 526 and stud 524 pair as depicted inFIG. 5's illustration of energy dissipation device embodiment 500.

FIG. 6 illustrates another embodiment of an energy dissipation deviceusing interlocks which do not provide lateral restraint to the filament,instead using additional components to provide the lateral restraint tothe filament. In particular, the energy dissipating device 600 includesa filament 610 extending between end-caps 640 and 640. At least oneend-cap 640 includes filament bracing components 620 surrounding thefilament 610 to provide lateral restraint to the filament 610 when thedevice 600 is in compression. In addition to the filament bracingcomponents 620, the device 600 includes rods 624 which include nuts 626or other stops located outward of the end caps 640 and 650. The nuts 626constrain translation of the end caps 640 and 650 away from one another,without constraining translation of the end caps 640 and 650 towards oneanother. These rods 624 allow the rods to add to the strength andstiffness of the device 600 when the device 600 is in tension, but willnot affect the strength and stiffness of the device 600 when the deviceis in compression. In other implementations, the rods 624 may be rigidlyattached to one of end caps 640 or 650, and extend through an aperturein the other end cap. In such an embodiment, only a single nut 626 perrod 624 on the outside of the unattached end cap would be required toconstrain translation.

These contact mechanisms, whether a part of the interlocks, or whether apart of a separate structure which does not provide lateral restraint tothe filament, may be constructed of any mechanical means suitable forthe particular design requirements of an instance of application. Whenthe contact mechanisms are a part of the interlocks, the contactmechanisms serve to bring the interlocks into contact when the device100, 400, 500 or 600 is put into tension. This contact will cause theinterlocks, in addition to the filament 110, 410, 510, or 610, to resisttensile deformations, adding both strength and stiffness to the device.When in compression, the contact mechanism will separate into thedeformation chamber 126, 426, or 526, or the rods 624 will extendthrough the end-caps 140 and 150 leaving only the filament 110, 410,510, or 610 to resist compressive deformations.

In embodiments such as those illustrate as devices 100, 400, 500, or600, whereupon the device maintains a higher strength and stiffness whenin tension than in compression, the device can behave as follows: In theinitial, undeformed condition, the interlocks can be of a length suchthat the contact mechanism is essentially in a relatively stress-freestate of contact. If the device is placed into tension, both thefilament and the interlocks can contribute to the stiffness that resiststhe tensile deformation. If, instead, the device is placed intocompression, the contact mechanism can separate, and the interlocks willbe unable to resist compressive forces. The separation of the contactmechanism can leave only the filament stiffness to resist compressiveforces. The mechanical behavior of the device being different in tensionthan in compression is the source of the asymmetric behavior withrespect to the force-displacement response.

If compressive deformation demand imposed on this implementation of thedevice by the surrounding dynamical system exceeds certain limitations,the filament will experience permanent, inelastic deformation (e.g.yielding), thereby reducing the stiffness of the device, reducing thestrength and stiffness of the system, and changing the dynamicalproperties of the system. This reduction in strength upon reaching acertain limit state provides a “fuse-like” effect to the dynamicalsystem. The device, when functioning as a fuse, can protect thesurrounding dynamical system from being overstressed by internal forcesgenerated from responses to external loading. This is a similar conceptto that of a plastic hinge at the ends of a concrete or steel framebeam.

The initial strength and stiffness behavior has been described for thisimplementation. The following is a description of its behavior duringcyclic loading: The compression of the filament is expected toexperience inelastic strains upon reaching a certain deformation limit.The combined tensile strength and stiffness of the filament andinterlocks may be designed to experience inelastic strains at a higherdemand than the filament alone, perhaps not experiencing inelasticstrain at all during cyclic demand. After a significant compressioncycle, upon load reversal, the filament will unload elastically along anunloading stress-strain relationship particular to the filamentmaterial. Prior to reaching the original undeformed device length, thefilament will be placed into tension. Depending on the magnitude of theprevious compressive inelastic strain, the filament may accumulatetensile inelastic strain, or it may still be deforming elastically, whenthe contact mechanism connects. Further tensioning of the device willthen engage both the filament and the interlocks, increasing both thestrength and stiffness of this particular embodiment of the device. Thecyclic inelastic straining of the filament provides hysteretic energydissipation for the surrounding dynamical system. This energydissipation will provide damping for the dynamical system, reducingdynamic response to system excitations.

This device may have numerous applications for systems that require afuse or energy dissipation but that also have requirements for onedisplacement direction to be stronger than the other. As an example,low-rise pre-engineered metal building moment frames are designed toresist both vertical and lateral building loads. The rafter-to-columnjoints have negative (closure-of-joint) bending moment demands due tosnow loads, dead loads, and roof live loads. A lateral load, such as aseismic excitation, can cause both negative and positive(opening-of-joint) bending moment demands on the same joints. Forlightweight structures, the vertical load demands can be larger inmagnitude than the seismic load demands. Therefore, if a typicalstructural fuse with symmetric behavior were utilized to dissipateenergy during a seismic event, one of two situations would occur. One,the symmetric fuse could be a fuse that provides a strength limitationduring a seismic event. However, because the fuse must be weaker thanthe seismic demands, it would also be weaker than the vertical loaddemands, taking damage from more loads than intended. Two, if thesymmetric fuse were strong enough to resist vertical load effects, itcould be too strong to deform and dissipate energy during a seismicevent, nullifying its purpose.

If placed in the rafter-to-column joint, diagonally between the outerflanges, in place of a standard web plate, a device embodiment whichpossesses greater strength and stiffness when in tension than incompression would create a truss to transfer bending moments from therafter to the column. The asymmetric device described would provide alarger strength and stiffness for moments due to vertical load effects,but under a seismic excitation, the device would dissipate energy whenplaced into compression by a positive bending moment.

FIG. 2 illustrates a cross-sectional view of an energy dissipationdevice which is configured to be stronger and stiffer in compressionthan in tension. This device embodiment 200 includes a filament 210extending through the receiving space 222 defined by the positions ofinterlocks 220. The interlocks 220 are configured such that they cannotoverlap each other when the device is compressed. The facing endsurfaces 223 of the interlocks 220 thus serve as contact surfaces which,when engaged with one another, constrain further lateral translation ofthe end-caps 240 and 250 towards one another. The filament 210 andinterlocks 220 are connected at each end of the device to the end-caps240 and 250 in a similar fashion as configuration 100.

The interlocks 220 will provide a continuous lateral restraint along thelongitudinal axis of the filament 210, except when the device 200 hasbeen tensioned and the interlocks 220 have separated. Note that theinterlocks 220 may be constructed from multiple parts.

The interlock configurations may be designed to provide adequate lateralrestraint to the filament to prevent said filament from buckling incompression. The quantified adequate lateral restraint is to bedetermined via structural mechanics and will consist of both strengthand stiffness requirements.

The interlocks 220 have a contact mechanism to provide contact when thedevice 200 is placed into compression. In some embodiments, the contactmechanism may take the form of a pair of contact surfaces 223 asdepicted in FIG. 2, but may be constructed of any mechanical meanssuitable for the particular design requirements of an instance ofapplication. The purpose of this contact mechanism is to bring theinterlocks 220 into contact during compression of the device 200. Thiscontact will cause the interlocks 220 to resist compressivedeformations, in addition to the filament 210, adding both strength andstiffness to the device. When in tension, the contact surfaces 223 willseparate, leaving only the filament 210 to resist tensile deformations.

In this implementation, the device 200 will behave as follows: In theinitial undeformed condition, the interlocks 220 will be of a lengthsuch that the contact mechanism is in a relatively stress-free state ofcontact. If the device 200 is placed into compression, both the filament210 and the interlocks 220 will contribute to the stiffness that resiststhe compressive deformation. If, instead, the device 200 is placed intotension, the contact surfaces 223 will separate and the interlocks 220will translate longitudinally away from one another. The separation ofthe contact surfaces 223 will leave only the filament 210 stiffness toresist tensile deformations. The mechanical behavior of the device 200being different in tension than in compression is the source of theasymmetric behavior with respect to the force-displacement response.

If tensile deformation demand imposed on this implementation of thedevice by the surrounding dynamical system exceeds certain limitations,the filament 210 will experience permanent, inelastic deformation (e.g.yielding), thereby reducing the stiffness of the device 200, reducingthe strength and stiffness of the system, and changing the dynamicalproperties of the system. The utility and the effects of this behaviorare similar to those of devices 100, 400, 500 and 600, describedpreviously.

The initial strength and stiffness behavior has been described. Thefollowing is a description of the behavior during cyclic loading: Thecombined filament 210 and interlocks 220 compressive strength may bedesigned such that inelastic strains are not experienced. However, thetension of the filament 210 is expected to experience inelastic strainsupon reaching a certain deformation limit. After a significant tensioncycle, upon load reversal, the filament 210 will unload elasticallyalong an unloading stress-strain relationship particular to the filament210 material. Prior to reaching the original undeformed device length,the filament 210 will be placed into compression. Depending on themagnitude of the previous tensile inelastic strain, the filament 210 mayaccumulate compressive inelastic strain or it may still be deformingelastically when the contact mechanism connects. Further compression ofthe device 200 will engage both the filament 210 and the interlocks 220,increasing both the strength and stiffness of the device 200. The cyclicinelastic straining of the filament 210 provides hysteretic energydissipation for the surrounding dynamical system. This energydissipation will provide damping for the dynamical system, reducingdynamic response to system excitations.

This device 200 may have numerous applications for systems which requirea fuse or energy dissipation but also have requirements for onedisplacement direction to be stronger than the other. Using the sameexample as for the embodiments described previously, low-risepre-engineered metal building moment frames are designed to resist bothvertical and lateral building loads. If the asymmetric device 200 isplaced in the rafter-to-column joint, diagonally between the outer andinner corners of the panel zone, in place of the standard web plate, thedevice 200 would create a truss to transfer bending moments from therafter to the column. The device 200 would provide a larger strength andstiffness for moments due to vertical load effects, but under a seismicexcitation, it would dissipate energy when placed into tension by apositive bending moment.

The embodiments described above differ from other structural fusemechanisms because they exhibit predictable and controlled asymmetricstrength and stiffness behavior in the load-deformation relationships.Some mechanisms in particular, which may resemble this device, arediscussed next in order to convey the differences between thosemechanisms and this device.

This device initially appears similar to a buckling restrained brace(BRB). The BRB consists of a similar filament surrounded by a shell.However, the shell is designed to simply provide continuous lateralbuckling restraint for the filament and does not resist structuralforces as do the interlocks. In addition, the BRB exhibits symmetricstrength and stiffness behavior with identical load-deformationresponses in both tension and compression.

Device 100 and 200 embodiments could possibly resemble a shock absorberor viscous damper in appearance. Since a shock absorber is also anenergy dissipation device, confusion between the utility of thesedevices could occur. However, a shock absorber works to dissipate energyby providing a resistance proportional to an imposed velocity and relieson pneumatic or hydraulic mechanisms for its functionality.

Finally, the brace of a concentric braced frame, used for resistinglateral loads in building systems, provides an asymmetricload-deformation behavior. It does this by buckling in compression andyielding along its longitudinal axis in tension. However, research hasshown that this buckling can cause high local bending strains leading tosignificant low-cycle fatigue. The compressive strength and stiffness ofthe concentric brace does not remain constant throughout deformation dueto buckling, nor can it be predicted accurately, and therefore cannot berelied upon to resist forces. Embodiments of energy dissipation devicesdisclosed herein, in contrast, can have tensile and compressive strengthand stiffness which is purposefully designed with high accuracy to meetthe force and deformation demands of the surrounding structural systemand will remain constant throughout excitation. Further, the embodimentsdescribed herein will be prevented from buckling by the filament bracingcomponents and will not exhibit the large local bending strains whichare problematic to the concentric braced frame system.

Although the invention has been described with reference to the aboveexamples, it will be understood that modifications and variations areencompassed within the spirit and scope of the invention. Accordingly,the invention is limited only by the following claims.

What is claimed is:
 1. An energy dissipation device, including: a firstretaining member, the first retaining member defining a first receivingspace; a second retaining member, the second retaining member defining asecond receiving space; a filament extending along a longitudinal axisthrough the first and second receiving spaces, the filament secured at afirst end to the first retaining member and secured at a second end tothe second retaining member; at least one of the first and secondretaining members being configured to constrain longitudinal translationof the first and second retaining members relative to one another toprovide an asymmetric force-displacement response to an induced axialload.
 2. The device of claim 1, wherein the second retaining member isconfigured to at least partially extend into the first receiving spaceof the first retaining member, and wherein at least one of the first andsecond retaining members includes a stop configured to inhibit removalof the second retaining member from the first receiving space of thefirst retaining member.
 3. The device of claim 1, wherein the firstreceiving space of the first retaining member includes a deformationregion in which the cross-sectional size of the first receiving spaceallows for the lateral translation of the second retaining member fromthe second receiving space into the first receiving space when acompressive axial load is applied to the device.
 4. The device of claim1, wherein a first end of the first retaining member is configured toabut a first end of the second retaining member to inhibit furtherlongitudinal translation of the first and second retaining memberseither towards or away from one another, depending on the desiredgeometric configuration.
 5. The device of claim 1, wherein the firstretaining member includes a first set of parallel plates and the secondretaining member includes a second set of parallel plates, and whereinthe second retaining member is configured to at least partially extendinto the first receiving space of the first retaining member.
 6. Thedevice of claim 5, wherein the filament and each of the plates in thefirst and second sets of parallel plates includes an aperture extendingtherethrough, and wherein the longitudinal dimensions of the aperturesin the first set of parallel plates is larger than the longitudinaldimensions of the apertures in the second set of parallel plates.
 7. Thedevice of claim 1, additionally including: a first end-cap secured tothe first retaining member and the first end of the filament; and asecond end-cap secured to the second retaining member and the second endof the filament.
 8. An energy dissipation device configured to providean asymmetric response to axial loading, the device including: an axialmember extending in a longitudinal direction between a first endcap anda second endcap; a bracing mechanism enclosing at least a portion of theaxial member, the at least one bracing member providing lateral supportto the axial member to inhibit buckling when the axial member is under acompressive load; a restraining mechanism configured to engage anothercomponent of the device to limit longitudinal translation of the firstand second endcaps relative to one another, such that other componentsof the device bear a portion of the axial load when the restrainingmember is engaged with another component of the device.
 9. The device ofclaim 8, wherein the bracing mechanism comprises first and secondretaining members, wherein the first endcap comprises or is coupled tothe first retaining member and the second endcap comprises or is coupledto the second retaining member, wherein the first retaining memberencloses a portion of the axial member adjacent the first endcap, andwherein the second retaining member encloses a portion of the axialmember adjacent the second endcap.
 10. The device of claim 9, wherein atleast one of the first and second retaining mechanisms includes acontact surface which serves as the restraining mechanism and isconfigured to engage a portion of the other of the first and secondretaining mechanisms to limit lateral translation of the first andsecond retaining mechanisms and allow the first and second retainingmechanisms to bear a portion of an axial load applied to the device. 11.The device of claim 10, wherein the contact surface comprises a surfaceof the first retaining member facing the second endcap and configured toabut a facing surface of the second retaining member to allow the firstand second retaining mechanisms to bear a portion of a compressive axialload applied to the device.
 12. The device of claim 10, wherein thecontact surface comprises a surface of the first retaining member facingthe first endcap and configured to engage an interlocking surface of thesecond retaining member to allow the first and second retainingmechanisms to bear a portion of a tensile axial load applied to thedevice.
 13. The device of claim 8, wherein the restraining mechanism isindependent of the bracing mechanism.
 14. The device of claim 13,wherein the restraining mechanism comprises: a second axial memberextending through an aperture in one of the first or second endcaps; andat least one stop coupled to the second axial member, wherein theapertures in one of the first or second endcaps is located between theof stop and the other of the first or second endcaps, and wherein across-sectional dimension of the stop is larger than a cross-sectionaldimension of the apertures such that the stop abuts an outer surface ofthe endcap including the apeture to limit longitudinal translation ofthe endcaps away from one another.
 15. A structural and/or mechanicalenergy dissipation device comprising: a first end-cap; a second end-cap;a filament extending between the first end-cap and the second end-cap,the filament comprising a material having nonlinear mechanicalproperties; a filament bracing component; and a restraining componentcomprising at least one contact surface configured to contact anotherportion of the device to limit further translation of the first end-caprelative to the second end-cap to provide an asymmetricforce-displacement response to an induced axial load.
 16. The device ofclaim 15, wherein the first end cap is rigidly attached to therestraining component and wherein the second end cap is movable over alimited range with respect to the restraining component.
 17. The deviceof claim 15, wherein a first cross-sectional dimension of the filamentis at least twice as large as a second cross-sectional dimension of thefilament.
 18. The device of claim 15, wherein the filament bracingcomponent includes at least two cantilevered members rigidly attached tothe first end-cap, wherein a length of the at least two cantileveredmembers is less than a length of the filament but at least half thelength of the filament.
 19. The device of claim 18, additionallyincluding at least two cantilevered members rigidly attached to thesecond end-cap, wherein the at least two cantilevered members, andwherein the at least two cantilevered members rigidly attached to thefirst end-cap and the at least two cantilevered members rigidly attachedto the second end-cap are configured to be freely translatable past oneanother when an axial load is applied to the device.
 20. The device ofclaim 15, wherein at least one of the filament and the restrainingmember comprises at least one of a metal, a shape memory alloy, or acomposite material.